When Am Yisrael left Mitzraim, the approximate number of Jewish males of Am Yisrael is mentioned. About 600,000. Due to the parallels between Am Yisrael's departure from Mitzraim and the Final Redemption, this number of 600,000 also comes up in relation to Kibbutz Galuyot.
Kol HaTor Chapter 6
Kibbutz Galuyot - How?
The work of Kibbutz Galuyot: How much is our obligation as messengers of the most High in the Atchalta DiGeulah? The minimum amount of Kibbutz Galuyot that has the power to return the Shechinah is at least the amount of "Population (Ochlusa) of Israel", i.e. 600,000. This number has the power to defeat the S'M in the gates of Yerushalayim. "For I will not enter in to Yerushalayim of Above until the Population of Israel enters in to Yerushalayim of below.
The following is the footnote on this paragraph.
And here it should be noted what is written in the Introduction to the Zohar Breishit and the explanation of Rav Moshe Maggid:
"In the Introduction to the Zohar on Sefer Breishit regarding the verse "Built Yerushalayim like a city which is connected together" it is written like this: "Thus I (Hashem) say to you (Yerushalayim): I will not go up Above until an Ochlusa will go up to you Below." And according to Chazal (Masechet Brachot 58) There is no Ochlusa less than 600,000. And a primary source for this we see in the words of the GR"A in the book Likutei HaGR"A (page 40 and Be'er Yitzchak there) that Kibbutz Galuyot is by the First Redeemer, Moshiach ben Yosef, and according to the verse "And the redeemed of Hashem will return and come to Tzion in joy" etc, and according to what is brought in the Gemara (Shabbat 88) that this verse is said about the number 600,000" - HaMaggid Doresh Tzion (p 64)
Rav Menachem Kasher, in his introduction to Kol HaTor in HaTekufah HaGedolah, mentions two statistical records:
5708 (1948) was the first year in centuries that there were 600,000 Jews living in Eretz Yisrael.
5727 (1967) was the first year in centuries that there were 600,000 Jewish males above the age of 20 living in Eretz Yisrael.
In short, the mere existence of this number is a tremendous Tikkun that is felt in the this world.
We are but a few years old away from the next Tikkun of Kibbutz Galuyot, having a majority of world Jewry in Eretz Yisrael. May we merit to see its benefits materialize in the physical world as well.